Brake control unit

ABSTRACT

Towed vehicles can be extremely heavy. Accordingly, it is too much of a burden to the braking system of a towing vehicle to not have brakes on the towed vehicle. Controlling the brakes of the towed vehicle must be accurately applied otherwise very dangerous conditions can be created. A method of controlling braking of a towed vehicle is, therefore, needed. The method comprises receiving speed signals based on speed of a towing vehicle, or a towed vehicle, or both said towing vehicle and said towed vehicle, receiving pressure signals based on pressure of a hydraulic brake system of the towing vehicle, and generating a brake output signal based on the speed signals and the pressure signals.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/689,420, filed on Aug. 29, 2017, entitled “Brake Control Unit,” whichis a continuation of U.S. patent application Ser. No. 14/330,944, filedon Jul. 14, 2014, now U.S. Pat. No. 9,758,138, entitled “Brake ControlUnit,” which is a continuation of U.S. patent application Ser. No.11/247,010 filed on Oct. 11, 2005, now U.S. Pat. No. 8,789,896, whichclaims priority to U.S. Provisional Patent Application No. 60/616,989filed on Oct. 8, 2004, which are all hereby incorporated by reference intheir entirety.

FIELD OF THE INVENTION

The present invention is generally related to a brake control unit, andmore particularly to a brake control unit for providing a brake outputsignal to brakes of a towed vehicle.

BACKGROUND OF THE INVENTION

A variety of prior art brake control units that provide a brake outputsignal to brakes of a towed vehicle, such as a trailer, have beenproposed and/or manufactured. A number of proposed brake control unitshave included a brake signal generator, e.g., a deceleration sensor,whose output has been utilized to determine a magnitude for the brakeoutput signal. In general, these brake control units have proposedutilization of a signal provided by a component, located within a towingvehicle, to determine a magnitude for a brake output signal that isprovided to brakes of a towed vehicle to initiate braking of the towedvehicle. However, disclosures associated with such proposed brakecontrol units have not disclosed how certain signals present on variousautomotive communication buses could be utilized to control and/oroptimize control of brakes of a towed vehicle. In particular, how speedsignals can be used to control and/or optimize control of the brakes ofthe towed vehicle.

When towed vehicles are traveling at slower speeds, the electric brakesused to stop or slow down such towed vehicles are often too aggressivecausing significant jerking, or in the worst case, locking of the brakesof the towed vehicle. What is needed, therefore, is a brake control unitthat is capable of applying a brake output signal to brakes of a towedvehicle that may be based on both a speed of a towing vehicle and asignal corresponding to the braking effort applied by the driver of thetowing vehicle, such as hydraulic pressure of a hydraulic brake systemof the towing vehicle. This would, therefore, permit the brake controlunit to reduce power to the towed vehicle brakes when it is traveling atlow speeds.

Further, it would be desirable for the brake control unit to determinecertain towed vehicle characteristics based on both a speed of a towingvehicle and a change in the speed of the towing vehicle or towed vehiclemeasured over a specific time period based on a known braking effort. Inaddition, it would be desirable for the brake control unit to create areal-time brake output signal based on estimated driving conditions tocompensate for variations in brakes of a towed vehicle that areattributable to a current speed of the towed vehicle.

Additionally, it would be desirable for the brake control unit toautomatically adjust the maximum magnitude of the brake output signaland/or provide a modified initial brake output signal and/or a modifiedslew rate of the brake output voltage, e.g., set a gain level and/orboost level. Finally, it would be desirable for the brake control unitto determine a towed vehicle characteristic based upon an actualdeceleration of a towed vehicle in response to a known output signal.

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to a method ofcontrolling braking of a towed vehicle. The method comprises receiving aspeed signal based on speed of a towing vehicle, or a towed vehicle, orboth the towing vehicle and the towed vehicle, receiving a pressuresignal based on pressure of a brake system of the towing vehicle, andgenerating a brake output signal based on the speed signal and thepressure signal.

According to another embodiment of the present invention, a method forcontrolling braking of a towed vehicle is disclosed. The methodcompromises periodically receiving speed signals based on speed of atowing vehicle, or a towed vehicle, or both the towing vehicle and thetowed vehicle, providing a brake output signal to brakes of the towedvehicle, estimating towing conditions of the towed vehicle based onchanges in the received speed signals attributable to the brake outputsignal, and modifying the brake output signal based on the estimatedtowing conditions to compensate for variations in the brakes of thetowed vehicle.

In yet another embodiment of the present invention, a method forcontrolling braking of a towed vehicle comprises periodically receivingspeed signals based on speed of a towing vehicle, or a towed vehicle, orboth the towing vehicle and the towed vehicle, increasing power suppliedby a brake output signal, e.g., a variable pulse width brake outputsignal, to brakes of the towed vehicle until a preset thresholddeceleration is achieved for the towed vehicle, determining reduction inthe speed signals over a fixed time period, determining a braking powerat which the preset threshold deceleration is achieved, and determiningcharacteristics of the towed vehicle based on the reduction in thespeed.

According to yet another embodiment of the present invention, a methodof controlling braking of a towed vehicle comprises receiving speedsignals based on speed of a towing vehicle, or a towed vehicle, or boththe towing vehicle and the towed vehicle, generating a brake outputsignal based on the received speed signals, the brake output signalbeing capable of being sent to the brakes of the towed vehicle,determining actual deceleration of the towed vehicle attributable to thebrake output signal, and determining characteristics of the towedvehicle based upon the actual deceleration of the towed vehicle.

According to yet another embodiment of the present invention, a methodof controlling braking of a towed vehicle comprises periodicallyreceiving speed signals based on speed of a towing vehicle, or a towedvehicle, or both the towing vehicle and the towed vehicle, estimating again setting of said towed vehicle based on the speed signals, anddetermining a maximum braking power before the wheels of the towedvehicle lock up under prevailing conditions of the towed vehicle basedon the estimated gain setting.

According to another embodiment of the present invention a method ofcontrolling braking of a towed vehicle comprises determiningdeceleration of at least one of a towed vehicle, or a towing vehicle, orboth the towing vehicle and the towed vehicle, determiningcharacteristics of said towed vehicle based upon said deceleration ofsaid towed vehicle, and modulating a brake output signal to periodicallyrelease and engage brakes of said towed vehicle, wherein the brakeoutput signal is based on the characteristics of the towed vehicle.

According to another embodiment of the present invention a method ofcontrolling braking of a towed vehicle comprises determiningacceleration of a towed vehicle perpendicular to direction of travel ofsaid towed vehicle, and modulating a brake output signal to periodicallyrelease and engage brakes of said towed vehicle based on saidperpendicular acceleration.

According to yet another embodiment of the present invention a method ofcontrolling braking of a towed vehicle comprises receiving adeceleration signal based on deceleration of at least one of a towedvehicle, or a towing vehicle, or both the towing vehicle and the towedvehicle, increasing power supplied by a brake output signal to brakes ofsaid towed vehicle until a present threshold deceleration is achievedfor said towed vehicle, determining a braking power at which the presetthreshold deceleration is achieved, and determining characteristics ofthe towed vehicle based on the deceleration.

These and other features, advantages and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an exemplary electrical block diagram of a brake control unit,according to an embodiment of the present invention;

FIGS. 2A-2B are an exemplary electrical schematic diagram of a brakecontrol unit, according to an embodiment of the present invention; and

FIG. 3 is a flowchart of an exemplary threshold routine, according to anembodiment of the present invention.

DETAILED DESCRIPTION

A brake control unit, according to an embodiment of the presentinvention, includes a processor and a memory subsystem. The brakecontrol unit is typically located within a passenger compartment of atowing vehicle, and may even be integrated with the towing vehicle. Forexample, the brake control unit may be integrated in the dash of thetowing vehicle. The processor is programmed to provide a brake outputsignal to brakes or brake load, e.g., electromagnetic brakes, of a towedvehicle responsive to one or more input signals, e.g., speed signals andpressure signals, that are provided by one or more automotive subsystemsof the towing vehicle. The automotive subsystems may be coupled to theprocessor via an analog interface, a parallel bus, or a serialcommunication bus, e.g., a controlled area network or high-speedcontrolled area network (CAN) bus. Alternatively, the input signals maybe provided by an automotive subsystem located on a towed vehicle orautomotive subsystems located both on the towing vehicle and the towedvehicle. Irrespective of the location of the automotive subsystem(s),the processor executes a routine to analyze the input signal(s) todetermine certain characteristics of the towing and/or towed vehicle,e.g., deceleration of a towing vehicle and, in turn, deceleration of atowed vehicle. This provides the ability of electric trailer brakes toachieve a desired deceleration that is highly dependent upon an initialspeed and load of an associated towed vehicle. Thus, a brake outputsignal may be tailored for a given initial towed vehicle speed and load,as well as road conditions to more readily achieve a desireddeceleration.

The processor is also coupled to the memory subsystem that storesvarious routines that allow the processor to perform various functions,e.g., automatically adjusting the maximum magnitude of the brake outputsignal and/or providing an increased initial brake output signal (suchas setting a gain and/or a boost function of the brake control unit) andto communicate with the automotive subsystem(s). The brake control unitmay also include a display, such as a dual seven-segment display, thatprovides status and diagnostic information to an operator of the towingvehicle.

The brake control unit may also provide a proportional brake outputsignal to the brakes when the towing vehicle is backing-up or a fixedbrake output signal when the towed vehicle is completely stopped withthe brake pedal depressed, e.g., on an incline. The brakes of the towingvehicle, therefore, are not required to stop or hold the towed vehiclewhen the towing vehicle is backing-up or is stopped on an incline.

As shown in FIG. 1 , a brake control unit 100 includes a processor 102coupled to a memory subsystem 104, a display 106, an automotivesubsystem 20, and a brake switching circuit 108. As used herein, theterm “processor” may include a general purpose processor, amicrocontroller, e.g., an execution unit with memory, etc., integratedwithin an integrated circuit, a digital signal processor (DSP), aprogrammable logic device (PLD), or an application specific integratedcircuit (ASIC), among other such processing devices. The processor 102may receive a manual input signal 101, a gain input signal 103, and/or aboost input toggle signal 105, among other input signals (notspecifically shown in FIG. 1 ).

A spring-biased wiper of a potentiometer coupled between a supplyvoltage, e.g., derived from a vehicle battery VBATT, and ground mayprovide the manual input signal 101 to the manual input of the processor102. It should be understood, however, that any other manual inputdevice can be used. This allows an operator of the towing vehicle toapply a brake output signal to the brakes 114 of the towed vehiclewithout engaging the brakes of the towing vehicle. Similarly, a wiper ofa rotary potentiometer coupled between a supply voltage, e.g., derivedfrom a vehicle battery VBATT, and ground may provide the gain inputsignal 103 to a gain input of processor 102. Again, it should beunderstood that any other manual input device can be used. The gaininput signal 103 allows an operator of the towing vehicle to adjust themaximum magnitude, e.g., the duty cycle, of the brake output signalprovided, via the brake load switching circuit 108, to the brake load114, e.g., brake electromagnets, of the towed vehicle.

According to one embodiment of the present invention, a boost switchcoupled to a boost input of the processor 102, when actuated, causes theprocessor 102 to toggle between normal operation and providing anincreased initial brake output signal to the brake load 114 of the towedvehicle. When a boost switch (SW1, see FIG. 2A) toggles the boost on,the processor 102 provides an initial brake output signal equal to afraction of the maximum brake output signal currently set by the gaininput signal 103. The boost switch may allow the operator to add anadditional brake output signal at the start of a braking event tocompensate for different towed vehicles, towed vehicle weight, or otherdifferent braking conditions, e.g., wet or dry road conditions. Theboost switch may also be used to modify the transfer function of thebrake control unit. This provides a faster slew rate of the output,which is especially useful for heavier towed vehicles. The boost switchallows the operator of the towing vehicle to provide a more aggressivebrake setting when the brake control unit is utilized with, e.g., heavymulti-axle trailers. Alternatively, a variable boost, e.g., set with apotentiometer, or incrementally stepped values can be employed.

The display 106 may take the form of a dual seven-segment display thatprovides information to the operator of the vehicle in the form ofalphanumeric characters, or any other configuration. As mentioned above,the automotive subsystem 20 provides an input signal to the processor102 that the processor 102 utilizes in determining a magnitude for thebrake output signal that is applied to the brakes 114 of the towedvehicle. As mentioned above, the brake output signal is applied by thebrake switching circuit 108, of which one embodiment is furtherdescribed below in conjunction with FIGS. 2A-2B. The automotivesubsystem 20 may take various forms, e.g., a global positioning system(GPS) receiver, a wheel speed sensor, an engine speed sensor, a throttleposition sensor, a Doppler sensor, etc. The automotive subsystem 20 maybe located within the towed vehicle, the towing vehicle, or within acombination of the towing and towed vehicles when multiple automotivesubsystems are used to provide multiple input signals.

Moving to FIGS. 2A-2B, an exemplary electrical schematic of a brakecontrol unit 200 is illustrated, according to one embodiment of thepresent invention. In the embodiment of FIGS. 2A-2B, the processor 102and the memory subsystem 104, of FIG. 1 , are implemented as amicrocontroller U5. The microcontroller U5 may receive a manual inputsignal (on pin 6) from a manual control, e.g., potentiometer, V1 and again input signal (on pin 8) from a gain control, e.g., a potentiometerV2. When a boost switch SW1 is present and asserted, a boost inputtoggle signal, as described above, may be received on pin 19 of themicrocontroller U5. A suitable microcontroller is manufactured and madecommercially available by Toshiba Corporation (part no. TMP87C809). TheTMP87C809 includes 8 K of internal read-only memory (ROM), two hundredfifty-six bytes of internal random access memory (RAM), six internal LEDdrivers, eight ten-bit analog-to-digital (A/D) converter channels, onesixteen-bit timer/counter, two eight-bit timer/counters and twenty-twoI/O ports. Alternatively, other microcontrollers having communicationbus interface capabilities, such as CAN interface capabilities, may beused to interface with the towing vehicle bus.

In operation, the microcontroller U5 monitors the towing vehiclestoplight switch (via connector P1, pin B) on pin 21 (via adivider/filter network including a resistor R8, a resistor R9 and acapacitor C6, whose values are, for example, 10 kΩ, 22 kΩ and 0.1 μF,respectively) to determine whether to implement various stored routines.The microcontroller U5 monitors the brake output signal (provided to thebrakes via connector P1, pin D and pin C (ground)) on pin 9 via adivider/filter network including a resistor R15, a resistor R22, and acapacitor C13, whose values are, for example, 22 kΩ, 10 kΩ and 4.7 μF,respectively.

The microcontroller U5 is programmed to periodically determine the speedof the towing vehicle by reading an analog level of a signal at pin 10,via a filter network including resistor R48 and capacitor C42, whosevalues are, e.g., 10 kΩ and 4.7 μF, respectively. Alternatively, thespeed may take the form of a digital signal and be provided to a serialport of the microcontroller U5 or may be provided via the towing vehiclecommunication bus, such as a CAN or a local interconnect network (LIN).In either case, the microcontroller U5 implements an algorithm thatperiodically reads a speed input (or an input from which the speed canbe derived). The speed input is used, at least in part, to determine amagnitude for a current brake output signal, e.g., a duty cycle of thebrake output signal, when a brake pedal of the towing vehicle isdepressed.

A change in the input signal, in general, indicates vehicle accelerationor deceleration in either a forward or reverse direction (whenbacking-up). When the microcontroller U5 determines that the currentinput signal(s) indicates the towing vehicle is not accelerating ordecelerating, the microcontroller U5 causes a brake output signal to beapplied to the brakes if the stop light switch is activated. When themicrocontroller U5 determines that the speed input is not changing andthat the stop light switch is still engaged, the microcontroller U5causes the brake output signal to ramp up to a voltage that is a fixedpercentage of a power control set point (set by the gain potentiometerV2, when implemented) after about four seconds, which produces a brakeoutput signal during stopped or static conditions. Alternatively, thegain control may be implemented using push button switch(es) and adisplay.

When the vehicle is stopped and the boost is on, the brake outputvoltage immediately steps to a fixed percent, e.g., twenty-five percent,of the power control set point. In one embodiment, when the boost switchSW1 is pressed during the ramp function, the boost switch SW1 takespriority and the output voltage immediately changes to twenty-fivepercent of the power control set point.

The microcontroller U5 may also receive another input signal, e.g., apressure input, on pin 7. The microcontroller U5 may utilize thepressure input in conjunction with the speed input to determine amagnitude for a brake output signal that is to be applied to the brakesof a towed vehicle, as is further discussed below. As is shown in FIG.2A, the analog pressure input signal is applied to a non-inverting inputof an operational amplifier U11 via a divider network that includes aresistor R46 and a resistor R45, whose values are, e.g., 11 kΩ and 10kΩ, respectively. A resistor R43, whose value is, e.g., 10 kΩ, iscoupled between an inverting input and output of the amplifier U11.

An output of a unity gain operational amplifier U12 is coupled to theinverting input of the amplifier U11 via a resistor R44, whose value is,e.g., 11 kΩ. A non-inverting input of the amplifier U12 is coupled to awiper of a potentiometer V3 (e.g., 5 kΩ) that is coupled between groundand to a positive voltage supply (e.g., +5 volts) via a resistor R41,whose value is, e.g., 21 kΩ. The output of the amplifier U11 is coupledto a non-inverting input of an operational amplifier U13 via a resistorR42, whose value is, e.g., 10 kΩ.

A potentiometer V4 (e.g., 50 kΩ) is coupled between ground and aninverting input of the amplifier U13, with a wiper of the potentiometerV4 being coupled to the inverting input of the amplifier U13. A filternetwork including resistor R47 and capacitor C41, whose values are,e.g., 12 Ω and 0.54 μf, respectively, is coupled between an output andthe inverting input of the amplifier U13. The output of the amplifierU13 is coupled to pin 7 of the microcontroller U5 via a filter networkthat includes a resistor R49 and a capacitor C43, whose values are,e.g., 35 kΩ and 4.7 μF, respectively. The circuit disclosed above isused to improve the dynamic range and resolution of the pressure signal.If, however, the resolution of the analog channel of the microcontrolleris sufficient, the pressure signal can be inputted directly to theanalog channel of the microcontroller using a protection circuit.

Alternatively, the pressure input signal may take the form of a digitalsignal and be provided to a serial port, communication bus, CAN bus, orLIN bus of the microcontroller U5. It should also be appreciated thatthe pressure input signal may take a variety of forms. For example, thepressure input signal may be provided by a brake pedal position sensor,a brake pedal pressure sensor pad, or a hydraulic brake system pressuresensor, among other such sensors. Irrespective of the sensor thatprovides the pressure input signal, the input signal provides anindication of the amount of braking intended, such as by using thehydraulic pressure of the hydraulic brake system of the towing vehicle,may be utilized by the microcontroller U5 in determining an appropriatebrake output signal.

The brake output signal may be provided in the form of a pulse widthmodulated (PWM) signal with a frequency of 250 Hz and a variable dutycycle, e.g., from zero to one-hundred percent. As shown in FIG. 2B, thebrake output signal is provided via high-side drivers U2 and U3, whichare coupled in parallel and switched by the microcontroller U5 (via pin12) through an NPN transistor Q7.

A resistor R23, e.g., 10 kΩ, limits the base current of transistor Q7and a resistor R4, e.g., 10 kΩ, pulls the collector of the transistor Q7to the vehicle battery VBATT (provided via connector P1, pin A) when thetransistor Q7 is turned off. The collector of the transistor Q7 is alsocoupled, through a current limiting resistor R5, e.g., 10 kΩ, to a gate(pin 2) of high-side drivers U2 and U3. A drain (pin 3) of the driversU2 and U3 is coupled to VBATT and a source (pin 5) of the drivers U2 andU3 is coupled to the brakes 114 (FIG. 1 ) of the towed vehicle. When thetransistor Q7 is turned on by the microcontroller U5, the drivers U2 andU3 are shut-off and a brake output signal is not provided to the brakes.When the microcontroller U5 turns the transistor Q7 off, the drivers U2and U3 are turned on and a brake output signal is provided to the brakes114 of the towed vehicle.

A suitable high-side driver is manufactured and made commerciallyavailable by ST Microelectronics (part no. VN920). The VN920 is a singlechannel high-side solid-state relay intended for driving any kind ofload with one side connected to ground. The VN920 incorporates aninternal charge pump that provides voltage to drive the gate of aninternal n-channel MOSFET to a voltage higher than VBATT. Thiseliminates the external charge-pump circuitry normally needed to drivean n-channel MOSFET. The VN920 also permits a one hundred percent dutycycle as a minimum off-time is not required to recharge a charge-pumpcapacitor.

The drivers U2 and U3 include a built-in current-sense circuit thatproduces a current from the sense pin (pin 4) that is proportional tothe current delivered to the load by the drivers U2 and U3. This currentsense output is monitored by the microcontroller U5 (pins 4 and 20) viaa filter network including a sense resistor R10, a resistor R3, and acapacitor C11, whose values are, e.g., 470 Ω, 10 kΩ and 3300 μF,respectively. This allows the microcontroller U5 to measure the currentdelivered to the load as well as determine whether a current overloadcondition exists with the brakes.

The microcontroller U5 also monitors the voltage across capacitor C5,via pin 5, to determine whether an open ground or short exists. Thevoltage across capacitor C5 is divided by resistors R7, e.g., 47 kΩ, andR13, e.g., 10 kΩ, before being provided to the microcontroller U5, suchthat the maximum input voltage to the microcontroller U5 is notexceeded.

Anytime the output is pulsed, current is delivered to the electromagnetsbuilding up energy in the magnetic field. When the pulse ends, thecurrent will continue to flow and charge capacitor C5. The voltageacross capacitor C5, therefore, rises above that of the vehicle batteryVBATT. If pulsing continues, the circuit can be damaged by excessvoltage. Therefore, when the voltage rises above a preset value, e.g.,18 volts, the microcontroller U5 is programmed to determine that thebrakes 114 are not operating properly and provides status information toan operator of the vehicle, via display DS1. When the voltage fallsbelow a preset value, e.g., 8 volts, the microcontroller U5 isprogrammed to determine that the brakes 114 are shorted and providestatus information to an operator of the vehicle via display DS1. Themicrocontroller U5 is programmed to provide appropriate information toan operator of the vehicle, via the display DS1, by illuminating anappropriate segment or segments and/or indicators of the seven-segmentdisplays. A suitable display is manufactured and made commerciallyavailable by FEMA (part no. DA20)

According to another embodiment of the present invention, themicrocontroller U5 is programmed to automatically set at least one of again level and a boost level for the brake control unit 200. Themicrocontroller U5 determines an appropriate gain level and/or boostlevel for the brake control unit 200 by performing a number ofprogrammed tasks. Initially, the microcontroller U5 causes a brakeoutput signal to be provided to the brakes of a towed vehicle when abrake pedal of a towing vehicle is depressed and before the brakes ofthe towing vehicle can respond to the depression of the brake pedal. Themicrocontroller U5 is also programmed to detect a deceleration of thetowed vehicle attributable to the brake output signal.

The detected deceleration provides an indication of towed vehiclecharacteristics, such as brake temperature, brake pad wear, proximity ofbrake pads to the brake drum, brake magnet strength, brake springstrength, brake pad moisture, battery voltage, number of axles, load oftowed vehicle, weight distribution of towed vehicle, tire conditions oftires of the towed vehicle, speed, etc. It also provides an indicationof the road conditions. It should be appreciated that a brake controlunit that is capable of automatically setting a gain level and/or aboost level does not require the potentiometer V2 or the boost switchSW1 and its associated components, e.g., resistor R18 and capacitor C12(see FIG. 2A). For example, if the speed signal of the towed vehicle isabout zero (meaning that the wheels of the towed vehicle are locked),the brake output signal is substantially equal to the reduced gainsetting. This means that the brake output signal corresponds to amaximum brake output signal that can be applied to the brakes of thetowed vehicles based on the towed vehicle characteristics. This reducedgain setting will continue to apply the reduced power to the brake loaduntil such gain setting is modified. Finally, the gain setting reducespower to the brake load irrespective of the pressure signals received.

It should be appreciated that even during rapid depression of a towingvehicle brake pedal there is a period of latency before hydraulic brakesof the towing vehicle are actually applied. Thus, if brakes of a towedvehicle are quickly ramped up after sensing a stoplight signal andbefore the hydraulic brakes of the towing vehicle can respond a “tug”that is a result of the towed vehicle brake initiation can be detected.This “tug” provides an indication of the onset of towed vehicle brakingand can be utilized to determine a desired boost level. This obviatesthe need for a separate boost switch that has generally been utilized tohelp a towed vehicle lead a towing vehicle in braking. Thus, when thevoltage ramp passes the point of onset of braking the ratio ofdeceleration to voltage change can be determined and utilized as a brakeeffectiveness coefficient. This provides a basis for automatic gain andboost control.

According to another embodiment of the present invention, a brake outputsignal, e.g., braking voltage, can be modulated at a given rate whiledeceleration is logged. This can be of particular assistance on surfaceswith a low coefficient of friction and with towed vehicles havinglighter loads that tend to result in locked wheels. This modulation is alow frequency modulation. It can be accomplished by sending a signal toperiodically release and engage the brakes of the towed vehicle to gainbetter control of braking of the towed vehicle. This creates a systemsimilar to an anti-lock brake system for the towed vehicle.Additionally, the brake control unit may also include a three-axisaccelerometer. This accelerometer can be used to determine theacceleration of the towed vehicle perpendicular to direction of travelof the towed vehicle. This signal is sent to the brake control unit andthe brake control unit modulates the brake output signal to periodicallyrelease and engage brakes of the towed vehicle based on theperpendicular acceleration. This can lead to a more suitable brakingevent for the towed vehicle.

As is discussed above, in brake control units that have a gain input, anoperator of the towing vehicle can adjust the maximum magnitude, e.g.,the duty cycle, of a brake output signal provided via the brakeswitching circuit to the brakes of a towed vehicle. Further, in brakecontrol units that have implemented a boost switch, the operator has anadditional brake output signal at the start of a braking event and canprovide a variable slew rate following that. This can compensate fordifferent towed vehicles, towed vehicle weight, or other differentbraking features, e.g., wet or dry road conditions. This can also allowan operator to provide a more aggressive brake setting when the brakecontrol unit was utilized with, e.g., heavy multi-axle towed vehicles.

According to one embodiment of the present invention, when a processorof a brake control unit determines that an input signal, e.g., a speedinput signal and/or a hydraulic brake pressure input signal, is notchanging and a towing vehicle stoplight switch is still engaged, theprocessor causes the brake output signal to ramp up to a voltage that isa fixed percentage of the power control set point. This may be set by again potentiometer after a predetermined period of time. This allows thebrake control unit to provide a brake output signal during stopped orstatic conditions. However, during certain conditions, such as withsteady application of a brake pedal of the towing vehicle on a verysmooth downhill grade, a brake control unit implementing such a rampfunction may implement the ramp function while the vehicle is moving. Asa speed signal provided by an automotive subsystem may provide noindication of movement.

Thus, in general, it is desirable to implement a braking control routinethat is capable of determining when a ramp function is implemented whilethe vehicle is in motion. One such braking control routine is disclosedin U.S. Pat. No. 6,615,125, entitled BRAKE CONTROL UNIT, which is herebyincorporated herein by reference in its entirety. This braking controlroutine determines if the ramp function is activated when the vehicle isin motion and acts to terminate the ramp function in such a case. In thepresent case, towed vehicle motion may be detected by evaluating whetheracceleration or deceleration is taking place by, e.g., monitoring aspeed input. By implementing a timer/counter or a time delay routine,the microcontroller U5 can determine whether the timer has exceeded await value. This is implemented to provide an indication that the towingvehicle is, in fact, stopped. If the timer/counter has exceeded the waitvalue, e.g., 4 seconds, the microcontroller U5 activates the rampfunction as described above. When the microcontroller U5 determines adeceleration exceeds a deceleration threshold the ramp function isterminated as this indicates that the towing vehicle is in motion.

According to another embodiment of the present invention, an automaticboost and/or gain routine can be implemented by providing a brake outputsignal to brakes of a towed vehicle while the towed vehicle is inmotion. In implementing an automatic boost and/or gain routine, themicrocontroller U5 determines whether a brake pedal of a towing vehicleis depressed. This is done in a matter similar to that described withrespect to FIGS. 2A and 2B above. If the brake pedal of the towingvehicle is depressed, the microcontroller U5 causes a brake outputsignal to be provided to brakes of the towed vehicle. Next, themicrocontroller U5 detects deceleration of the towed vehicle that isattributable to application of the known brake output signal. In thismanner, the microcontroller U5 can determine the relationship betweenthe detected deceleration and the known brake output signal. Thedeceleration of the towed vehicle, with respect to a given brake outputsignal, provides an indication of the towed vehicle characteristics suchas The detected deceleration provides an indication of towed vehiclecharacteristics, such as brake temperature, brake pad wear, proximity ofbrake pads to the brake drum, brake magnet strength, brake springstrength, brake pad moisture, battery voltage, number of axles, load oftowed vehicle, weight distribution of towed vehicle, tire conditions oftires of the towed vehicle, speed, etc. It also provides an indicationof the road conditions. Thus, the ratio of the deceleration to the brakeoutput signal can be associated with an appropriate value in, e.g., alook-up table that is utilized by the microcontroller U5 to determine anappropriate boost level and/or gain level for the brake control unit.

According to another embodiment of the present invention, themicrocontroller U5 may be programmed to automatically control braking ofa towed vehicle responsive to multiple inputs. For example, themicrocontroller U5 may receive speed signals that are indicative of aspeed of at least one of a towing vehicle and a towed vehicle, and abrake signal that is indicative of a hydraulic pressure of a hydraulicbrake system of the towing vehicle. The microcontroller U5 then respondsby applying a brake output signal whose magnitude is based on both thespeed and the brake signal to brakes of the towed vehicle.

An exemplary algorithm for implementing such a program is set forthbelow:VOUT=f1(VBP)*f2(SPEED)*TBC*f3(GAIN)where VOUT is the magnitude of the brake output signal, e.g., betweenzero and twelve volts; TBC is 1 if the towed vehicle brakes are sensedand 0 if the towed vehicle brakes are not sensed; GAIN is greater thanzero and less than or equal to one; VBP is a scaled value of thehydraulic brake pressure signal, e.g., between zero and five volts; andSPEED is a scaled value of the speed signal provided by a sensor locatedin the towing/towed vehicle. It should be understood, however, that thisalgorithm is merely an exemplary embodiment and that other algorithmsare contemplated herein.

In another embodiment, the microcontroller U5 is also programmed todetermine a relationship between the speed and a speed threshold. Themicrocontroller U5 is programmed to modify the brake output signal toprovide less power to the brakes as a function of the speed when thespeed is below the speed threshold, e.g., 25 kilometers/h. In anotherembodiment, the microcontroller U5 is programmed to modify the brakeoutput signal to provide power to the brakes as a function the pressure.In yet another embodiment, the microcontroller U5 is programmed tomodify the brake output signal to provide power to the brakes as afunction of the speed and as a function of the pressure.

With reference to FIG. 3 , a threshold routine 300 is initiated at step302. At step 304 the microcontroller U5 receives a speed signal from,e.g., a GPS receiver. Next, in step 306 the microcontroller U5 receivesa pressure signal from, e.g., a hydraulic brake system pressure sensor.As the brake signal output is a function of both the brake pressure andthe towing vehicle speed, the brake signal output is first calculated asa function of the brake pressure. Accordingly, at step 308 themicrocontroller U5 calculates the brake output signal as a function ofthe brake pressure, which is OUTPUTpr. OUTPUTpr is a substantiallynon-linear or piecewise linear function of the brake pressure. Next, atstep 310, the microcontroller U5 calculates a multiplying factor (MF)based on the speed signal. The MF is less than 1. Then, at step 312 themicrocontroller U5 modifies the OUTPUTpr by multiplying it with MF. Thisresults in the appropriate brake output signal, which is applied to thebrakes of the towed vehicle at step 314. It should be noted that MF is asubstantially non-linear or piecewise linear function of the speed.Thus, in general, VOUT=f1(brake pressure)*f2(speed), where f1 and f2 aresubstantially non-linear or piecewise linear functions.

It should be appreciated that the speed signals may be provided byvarious sources, e.g., a global positioning system (GPS) receiver, awheel speed sensor, an engine speed sensor, a throttle position sensorand a Doppler sensor. Such sources may be interfaced with themicrocontroller via analog channel, CAN bus, LIN bus, or serialcommunication.

According to yet another embodiment, the microcontroller is programmedto determine an actual deceleration of the towed vehicle based upon thespeed signals and determine a towed vehicle characteristic, based uponthe actual deceleration of the towed vehicle. Alternatively, the actualdeceleration of the towed vehicle may be determined using a deceleromterinterfaced with microcontroller. Regardless of the method used, themicrocontroller U5 then causes the brake output signal to be adjusted toachieve a desired deceleration for the towed vehicle. The towed vehiclecharacteristic may include, without limitation, brake temperature, brakepad wear, proximity of brake pads to the brake drum, brake magnetstrength, brake spring strength, brake pad moisture, battery voltage,number of axles, load of towed vehicle, weight distribution of towedvehicle, tire conditions of tires of the towed vehicle, speed, etc. Italso provides an indication of the road conditions.

According to another embodiment, the microcontroller U5 is programmed toperiodically receive speed signals that are indicative of a speed of atowing vehicle and/or a towed vehicle. The microcontroller U5 is furtherprogrammed to increase power supplied by a variable brake output signalto the brakes of the towed vehicle until a preset thresholddeceleration, e.g., −2 m/s2 is achieved for the towed vehicle. Next, themicrocontroller U5 determines a braking power at which the presetthreshold deceleration is achieved. The microcontroller U5 alsodetermines a towed vehicle characteristic based on both the speed signaland a known braking time in which the preset threshold deceleration isachieved. For example, if the change in deceleration compared with thechange of time is above a certain threshold, e.g., 25 kilometers perhour, the microcontroller U5 can determine the status of the brakes,e.g., are they heated and/or are they aligned properly.

According to still another embodiment, the microcontroller U5 isprogrammed to periodically receive speed signals that are indicative ofa speed of a towing vehicle and/or a towed vehicle. The microcontrollerU5 is further programmed to provide a brake output signal to brakes ofthe towed vehicle. In this manner, the microcontroller U5 can estimatedriving conditions as seen by the towed vehicle based on changes in thereceived speed signals attributable to the brake output signal. Inresponse to the estimated driving conditions the microcontroller U5 thencreates a second, real-time brake output signal to compensate forvariations in brakes of the towed vehicle that are attributable to acurrent speed of the towed vehicle. The microcontroller may estimatedriving conditions by determining a braking effectiveness for the towedvehicle braking based on a reduction in value of the received speedsignals. It then adjusts a pulse width of the brake output signal basedupon the effectiveness of the towed vehicle braking. In this manner, themicrocontroller U5 provides a real-time brake output signal furthermodified by the previous output signal that also compensates forvariable towed vehicle characteristics. Additionally, themicrocontroller U5 can assess and compensate for the load of the towedvehicle and the current road condition even when no braking event isoccurring so long as too much power is not sent.

According to yet another embodiment, the microcontroller U5 isprogrammed to receive speed signals indicative of a speed of a towingvehicle and/or a towed vehicle and apply a brake output signal to brakesof the towed vehicle. The microcontroller U5 then determines an actualdeceleration of the towed vehicle attributable to the brake outputsignal and based upon the received speed signals. The microcontroller U5then determines a towed vehicle characteristic based upon the actualdeceleration of the towed vehicle.

According to another embodiment, the microcontroller U5 is programmed todetermine a speed of a towing vehicle and/or a towed vehicle, determinea pressure of a hydraulic brake system of the towing vehicle, and applya brake output signal to brakes of the towed vehicle. In thisembodiment, power provided to the brakes by the brake output signal is afunction of the speed and the hydraulic pressure. In a relatedembodiment the microcontroller U5 also determines a relationship of thespeed of the towing vehicle and a speed threshold and modifies the brakeoutput signal to provide less power to the brakes as a function of thespeed when the speed is below the speed threshold. In addition, themicrocontroller U5 modifies the brake output signal to provide power tothe brakes as a function of the pressure.

In another different embodiment, the microcontroller U5 periodicallyreceives speed signals that are indicative of a speed of a towingvehicle and/or a towed vehicle. The microcontroller U5 also causes abrake output signal to be provided to brakes of the towed vehicle. Themicrocontroller U5 then determines an actual deceleration of the towedvehicle attributable to the brake output signal based upon a change inthe speed of the towing vehicle or by using a deceleration signal froman accelerometer. The microcontroller U5 uses the actual deceleration ofthe towed vehicle to estimate towing conditions seen by the towedvehicle. The microcontroller U5 then determines a pressure of ahydraulic brake system of the towing vehicle and the real-time brakeoutput signal is further modified based on the estimated drivingconditions, the hydraulic pressure, and current speed of the towedvehicle.

Modification of the invention will occur to those skilled in the art andto those who make or use the invention, including, without limitation,the values provided for the various elements disclosed above. It shouldbe understood that such values are exemplary values and the presentinvention is not limited to those values. Therefore, it is understoodthat the embodiments shown in the drawings and described above aremerely for illustrative purposes and not intended to limit the scope ofthe invention, which is defined by the following claims as interpretedaccording to the principles of patent law, including the Doctrine ofEquivalents.

The invention claimed is:
 1. A method of controlling braking of a towedvehicle, the method comprising: receiving a speed signal from anautomotive subsystem based on a speed of at least one of a towingvehicle and a towed vehicle; sending a brake output signal from aprocessor based on the speed signal to brakes of the towed vehicle toprovide power to the brakes; applying a function to modify the brakeoutput signal only when the speed of at least one of the towing vehicleand the towed vehicle is below a speed threshold, wherein the functionmodifies the brake output signal based on the speed of at least one ofthe towing vehicle and the towed vehicle; and wherein the brake outputsignal is not modified based on the speed of at least one of the towingvehicle and the towed vehicle when the speed of at least one of thetowing vehicle and the towed vehicle is above the speed threshold. 2.The method of claim 1, wherein the speed of the towing vehicle or thetowed vehicle or both the towing vehicle and the towed vehicle isdetermined based on at least one of a global positioning systemreceiver, a wheel speed sensor, an engine speed sensor, a throttleposition sensor, and a Doppler sensor.
 3. A method of controllingbraking of a towed vehicle, the method comprising: receiving an inputsignal based on a pressure in a brake system of a towing vehicle;generating a brake output signal based on the input signal from aprocessor; sending the brake output signal to brakes of the towedvehicle to provide power to the brakes; receiving a speed signal basedon a speed of at least one of the towing vehicle and the towed vehicle;determining a relationship between the speed of at least one of thetowing vehicle and the towed vehicle and a speed threshold; applying afunction to modify the brake output signal only when the speed of thetowing vehicle is below the speed threshold; and wherein the functionmodifies the brake output signal based on the input signal.
 4. Themethod of claim 3, wherein the speed of the towing vehicle or the towedvehicle or both the towing vehicle and the towed vehicle is determinedbased on at least one of a global positioning system receiver, a wheelspeed sensor, an engine speed sensor, a throttle position sensor, and aDoppler sensor.
 5. A method of controlling braking of a towed vehicle,the method comprising: determining a deceleration of at least one of atowing vehicle, or a towed vehicle, or both the towing vehicle and thetowed vehicle; determining the speed of the towing vehicle or the towedvehicle or both the towing vehicle and the towed vehicle; and modulatingthe brake output signal to periodically release and engage the brakes ofthe towed vehicle, wherein the brake output signal is based at least inpart on the speed of the towing vehicle or the towed vehicle or both thetowing vehicle and the towed vehicle.
 6. The method of claim 5, whereinthe speed of the towing vehicle or the towed vehicle or both the towingvehicle and the towed vehicle is determined based on at least one of aglobal positioning system receiver, a wheel speed sensor, an enginespeed sensor, a throttle position sensor, and a Doppler sensor.
 7. Themethod of claim 5, further comprising: determining a hydraulic pressureof a hydraulic brake system of the towing vehicle; and modulating thebrake output signal to periodically release and engage the brakes of thetowed vehicle, wherein the brake output signal is based at least in parton the pressure of the hydraulic brake system of the towing vehicle. 8.The method of claim 7, wherein the hydraulic pressure is determinedbased on at least one of a hydraulic pressure sensor, a brake pedalsensor, a brake pad sensor, and a signal from a communications bus.